The concept of multiplexing packet data flows, including realtime transport protocol (RTP) flows together into a single aggregate flow is a concept that is addressed in a number of Internet engineering task force (IETF) Internet drafts. Multiplexing RTP flows would be desirable, because it can reduce the bandwidth usage of wide area network (WAN) links and decrease the RTP packet rate incident on edge routers. In addition, the multiplexing of RTP flows reduces the burden of administering networks, for example in connection with the configuration of quality of service levels. In addition, multiplexing RTP flows can increase the scalability of existing quality of service schemes.
Although IETF Internet drafts specifying packet formats for aggregate flows, header compression algorithms, and packet loss compensation have been proposed, there are no methods discussed for signaling to a multiplexer which RTP flows to aggregate into a single flow. Although a multiplexer could examine individual RTP flows to determine which packets are candidates for aggregation, doing so would be a significant burden on the multiplexer. In particular, an RTP multiplexer in such a system would be required to examine the destination addresses of individual packets to determine whether they could be aggregated with other packets for transport to another multiplexing device for deaggregation back into individual flows or packets. In addition, requiring a multiplexer to consider the destination addresses of individual packets to determine whether aggregation would be beneficial introduces additional latency into data streams. The addition of latency is particularly undesirable in connection with voice over Internet protocol (VoIP) sessions and may require the addition of costly hardware to the multiplexing device to mitigate or avoid. Furthermore, where explicit information regarding the flows that should be aggregated is not provided to a multiplexer, indeterminancy regarding which flows are aggregated is introduced into the system. This indeterminancy can contribute to delays while the multiplexing devices wait for expected packets that never arrive.